Many procedures involving the preparation of biological cells for analysis require that unreacted reagents and cellular debris be separated from the cells of interest. Traditionally batch centrifugation has been the method of choice to perform this separation. However, batch centrifugation is not readily adaptable to automated sample preparation systems.
Most automated sample preparation equipment utilize circular or rectangular arrays of disposable test tubes. The test tubes are transported to appropriate positions so various operations can be performed sequentially and discretely on each test tube. In many sample preparation procedures, the time between discrete operations must be carefully controlled to obtain reliable and reproducible results. However, the operation of cell washing by centrifugation, as it is practiced in the art, is a batch operation. This batch operation cannot be performed sequentially and discretely on each test tube. The presence of a batch operation by definition disrupts the timing of the discrete operations which precede and follow the batch operation.
Batch centrifugations require substantially equal volumes of liquid in each tube to balance the centrifuge rotor, which may not always be desirable in an automated sample preparation system.
Batch centrifugations require rotational alignment of the centrifuge rotor with the loading/unloading system which introduces additional complexity into the centrifuge drive. Samples also require positive sample identification after centrifugation to verify rotational alignment was achieved.
Lastly, the centrifuge rotor and loading/unloading apparatus increases the size, weight and complexity of the system.
In spite of these limitations, automated sample handling systems that utilize batch centrifugation do exist. The ASHS system, marketed by Automed, automates the loading and unloading of conventional centrifuges using robotics; however such systems are large and costly, and only suitable for high volume laboratories.
Another category of instruments has been developed for blood washing and processing, as described in U.S. Pat. Nos. 5,405,308, 4,983,158, 4,668,214, 4,300,717, and 4,086,924. Generally these instruments consist of a bowl assembly with a central feed tube to introduce blood or wash solution to the bowl, feed tube and seal assembly which provide an input feed line to the bowl and an output line from the bowl, and a core assembly that imparts angular velocity to the incoming fluid. These instruments are not suitable for cell washing in automated sample preparation equipment because they require specialized bowl/core structures to enhance the processing of large quantities (ca 500 ml) of undiluted blood.
A number of companies market automatic cell washers. One such system, the Centra-W Automatic Cell Washer marketed by IEC, automate the aspiration of supernatant and addition of dilutent, but still require manual loading and unloading of the sample containers into and from the centrifuge rotor. Consequently, these types of instruments are not compatible with automated sample preparation equipment.
It would be desirable to have a method and apparatus to wash cells that are compatible with automated sample preparation equipment. Such a method and apparatus should operate on each sample individually so it can be synchronized with the other discrete operations performed on the samples.
It would also be desirable to have an apparatus that could be implemented as a discrete processing station on the periphery of a carousel or linear track sample preparation system.
Furthermore, it would be desirable to perform the wash step in the same disposable test tubes commonly used in automated sample preparation and analysis equipment.
It would also be desirable for the cell washer to effectively wash out the undesired cellular debris and unreacted reagents, and to concentrate the desired cells.
Lastly, it would be desirable to have the cell washer apparatus operate without an elaborate system to transport the sample containers to and from the cell washing apparatus.